Crystals utilizing total internal reflection or attenuated total reflection (ATR) principles are well known in optical systems for analyzing samples by determining the optical constants thereof and by establishing the physical and chemical composition thereof. Examples of ATR crystals in various optical systems are shown, for example, in U.S. Pat. Nos. 4,602,869 and 3,393,603. These ATR crystal optical systems utilize rather complicated optical paths, which limit the flexibility of those systems and limit the type and size of sample that can be analyzed.
An example of such an ATR crystal system is disclosed in an article appearing in the June, 1988 issue of the Spectroscopy magazine. A nano-sampler, apparently offered by Harrick Scientific Corporation, is pictured and described in that article. As pictured, an internal reflection crystal has a fibrous sample positioned against part of a sampling surface. A mask is selectively positioned at, or very near, the sample plane to allow selected energy reflected from the sample to escape from the crystal and pass through the output side of the optical system to a detector. A visible light viewing system is positioned above the sampling surface apparently to allow the sample, sample surface and sample plane to be observed to assist in positioning the sample and mask at the sample plane. The ATR crystal is set up in this optical system to act like a light pipe in directing energy therealong to the angularly positioned sample surface at one end thereof. The Harrick optical system is rather complicated and does not allow any visible light viewing through the ATR crystal to the sample.